<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Canvas</title>
    <style>
      body {
        margin: 0;
        overflow: hidden;
      }
    </style>
  </head>
  <body>
    <canvas class="myCanvas">
      <p>添加恰当的反馈信息。</p>
    </canvas>
    <script>
      var canvas = document.querySelector('.myCanvas');
      var width = canvas.width = window.innerWidth;
      var height = canvas.height = window.innerHeight;
      var ctx = canvas.getContext('2d');
      ctx.fillStyle = 'rgb(0, 0, 0)';
      ctx.fillRect(0, 0, width, height);
    </script>
  </body>
</html>